3.1 The Quadrilateral Position
Marquadt’s claim that Wesley bases his arguments outside Scripture seems to come from his statement:
“I would now inquire, whether these things can be defended, on the principles of even heathen honesty; whether they can be reconciled (setting the Bible out of the question) with any degree of either justice or mercy.”
Marquadt sees this as an argument based upon Natural Justice. In other words, it might be said that he is arguing from ‘Reason’ where reason means “what within your culture you consider reasonable.”
Why might Wesley choose to do this? The Wesleyan Quadrilateral would suggest that Wesley sees this as the most appropriate authority in this context. This might be argued first by reference to his understanding of Scripture’s Authority and secondly by reference to his understanding of Experience.
3.1.1. By reference to the Authority of Scripture
Jones argues that, “Wesley never suggests that the Bible contains all we need to know on every subject of human knowledge.” So, for example, “Wesley’s scientific interests are governed by the empirical method of his time, and not by proofs drawn from Scripture.” This might imply a ‘Two Kingdoms’ approach to revelation where special revelation deals specifically with the church and salvation but there is “a common, natural moral standard to which Christians, members of the spiritual kingdom, should ordinarily appeal when interacting with others in their lives in the civil kingdom.”
Where Scripture does speak about a subject, Wesley’s primary concern is to ensure that his interpretation of each passage conforms “to the whole scope and tenor of Scripture.” Jones equates this to “the analogy of faith” common within Protestant circles. Wesley thinks that there is a narrative running through Scripture and our interpretation of individual texts should be subject to this. The question then is what happens when his interpretation doesn’t fit the overall tenor. Wesley answers that question in his sermon on “Free Grace.” That sermon set Wesley at odds with Whitfield over the subject of Predestination. With regards to those texts quoted in support of eternal Election, Wesley argues:
“Whatever that Scripture proves, it never can prove this. Whatever its true meaning be, this cannot be its true meaning. Do you ask ‘What is its true meaning then?’ If I say, ‘I know not,’ you have gained nothing. For there are many Scriptures the true sense neither you nor I shall know till death is swallowed up in victory. But this I know; better it were to say it had no sense at all than to say it had such a sense as this.”
We might suppose, then, that something similar happens with regards to slavery. For reasons that we will outline below, Wesley regarded the trade to be incompatible with the “tenor of Scripture.” However, when it came to specific Scripture texts on the subject, it was not possible for him to build a case for abolition. Indeed, if Marquadt is right then:
“Neither the Old Testament nor any of the Gospels contain any fundamental protests against slavery; in fact, many passages assume its existence as a given. The Church has repeatedly appealed to such passages to justify its renunciation of social change.”
Therefore, it might be suggested that Wesley leaves Scripture to deal with the general principles of redemption whilst drawing on Reason for the specific arguments relating to ethical questions such as slavery.
3.1.2. By reference to Experience
In a letter to Granville Sharpe dated October 11th 1787, Wesley claimed that “Ever since I heard of it first I felt a perfect detestation of the horrid Slave Trade.” Roy Hattersley thinks that Wesley is being a little bit disingenuous. It is true, he argues, that “Wesley certainly felt compassion for those among them who were mistreated.” However, “there is no evidence that the Georgia missionary ever thought about emancipation” until “Sharp and Funnel stirred the conscience of the nation.”
Wesley’s view does appear to have changed over time. On the one hand, he never seems to regard slaves as second class citizens in the sense that the possibility of redemption was never closed to them. His Journal Entry of the 31st July 1736 tells how he “was glad to see several Negroes at church” when he first arrived in Charlestown. The same entry tells of his unsuccessful attempt to engage them in religious instruction.
However, the Journal is for the most part silent on the subject of slavery. His colleague, Whitfield, defended ownership but, unlike with their sharp disagreement over predestination, there appears to be no record of a dispute over this matter. Furthermore, Wesley’s entries regarding early meetings with John Newton do not raise the subject of slavery.
More explicitly, he seems to allow for some forms of slavery in his Explanatory notes, explaining with regards to Exodus 21:20 that “Direction is given what should be done, if a servant died by his master’s correction. This servant must not be an Israelite, but a Gentile slave, as the Negroes to our planters.”
His publication of “Thoughts” in 1774 appears to be his first significant contribution on the other side of the debate. So what brought about the change? The argument above would suggest that Reason plays a strong part but there seems to be more to it than a cold engagement with the rational arguments of campaigners.
We might then trace the influence of experience on his opposition to slavery both through his own observations of its effects and in the accounts he reads. First, we see in his reading of those accounts a response that is both intellectual and emotional. His reading of one slave’s account on the 24th of February 1791 prompts him to write what proved to be his last letter to Wilberforce, encouraging him in the struggle.
Secondly, with regards to his own experience, we might identify his frustration, even back in Georgia, at the slaves’ lack of spiritual knowledge. In “Thoughts” he lays the blame for this ignorance at the door of the owners. Does Wesley see a connection between their reluctance and his previous position on Exodus 20? If a heathen slave is permitted by analogy to the Jew-Gentile distinction, then his conversion is not in the owner’s interest.
It is certainly the case that Wesley sees a connection between their physical and their spiritual slavery, praying at the end of “Thoughts,” “O burst thou all their chains in sunder; more especially the chains of their sins! Thou Saviour of all, make them free, that they may be free indeed!” Furthermore, Clarkson makes a similar connection, accusing his opponents of “unwillingness to convert them to Christianity, because you suppose you must use them more kindly when converted.”
3.2. Response in support of the thesis
To understand why Wesley makes the move he does, we need to establish a correct understanding of his use of Reason and Experience. First, we need to deal with a general misconception about what is meant by Experience. For Wesley, this is not a private, subjective experience, governing interpretation of Scripture. Rather, it is comparable to what Wilberforce calls “the practical influence of religion.” Wesley talks about Experience in order to counter “formalism.” He believes that there is a practical outworking in response to Scripture seen in terms of the indwelling of the Holy Spirit, the work of sanctification and Assurance.
Secondly, Reason does not exist as a body of culturally conditioned knowledge. Rather, “it means a faculty of the human soul; that faculty which exerts itself in three ways: by simple apprehension, by judgment and by discourse.” It is this faculty, “(assisted by the Holy Ghost) which enables us to understand what the Holy Scriptures declare concerning the being and attributes of God.”
The implication of this is that there are two groups of people. There are those who, by the Holy Spirit’s enabling, are willing and able to understand and submit to Scripture and there are those who are not. Therefore, with regards to the second group, Wilberforce argues “I cannot persuade myself that they are so much under the practical influence of religion, that if they should convince their understandings, we should alter their conduct.” This makes him unwilling to engage with them in a discussion about Scripture. I would suggest that Wesley is exhibiting the same reluctance.
How then can a conversation take place with the wider public? Both Wesley and Wilberforce clearly regard this as possible, otherwise their writing is in vain. The answer is that even for those who reject Scripture, “Those great principles” are…”manifest in them; for God hath showed it to them – By the light which enlightens every man that cometh into the world.” 
In one sense this is a resort to Natural Law as suggested above, but not in the sense that Wesley allows for a separate sphere of revelation independent from Scripture. There are a number of reasons for concluding this. First, because of how Wesley does interact with Scripture and secondly because his argument here is really a concession within a particular and constrained context.
This is best seen by answering the question of what exactly are “these things” which relate to justice and mercy? The answer is that they are the elements of his opponents’ argument; namely that the nature of the trade is compatible with justice and mercy. It is compatible with justice because slavery is legitimate in three situations:
- When slaves taken captive in war (because taking captives is necessary within warfare in the same way that killing is).
- When a slave sells himself. 
- When someone is born into slavery. 
The slavers argue that their position is compatible with mercy because it is in order to rescue men and women from death that they take them.
Wesley, therefore, responds by demonstrating first that the argument from justice falls down by reference to legal theory. He quotes from Judge Blackstone to show first that the justification for killing and taking prisoners in wartime cannot be extended to maintaining their captivity after war because:
War itself is justifiable only on principles of self-preservation: Therefore it gives us no right over prisoners, but to hinder their hurting us by confining them. Much less can it give a right to torture, or kill, or even to enslave an enemy when the war is over.
With regards to those who sell themselves into slavery, he argues that it is not possible to sell yourself but only your labour because it would not be possible for the buyer to provide appropriate consideration for an entire life. So of course, if the first two justifications fall, then so does the third as it is dependent upon the first two. 
Secondly, he refutes their appeal to mercy as a justification because it is their desire for slaves which leads them to induce the behaviour amongst the inhabitants of Africa which leads to the threat of death.
The important thing to note then is that it is not Wesley who raises the argument from Natural Law principles. Rather, it is his opponents. Wesley is responding to them. In effect, he engages in a form of thought exercise asking the question “Suppose I were to allow you to argue on your terms without reference to Scripture, would that destroy my case?” Wesley’s conclusion is that “even” by reference to “principles of…heathen honesty” their argument fails.
 Italics mine. Wesley, Thoughts Upon Slavery, (IV.1), 29.
 Johnston, Reel Spirituality, 113.
 Jones, John’s Wesley’s Conception and Use of Scripture, 38.
 Jones, John’s Wesley’s Conception and Use of Scripture, 40.
 David VanDrunen, A Biblical Case for Natural Law (Grand Rapids, Michigan: Acton Institute, 2001), 45.
 Wesley, Sermons III: 71-114. (Vol 3 of The Works of John Wesley; Edited by Albert C Outler. Nashville, Tennessee: Abingdon Press, 1986), 552.
 Jones, John’s Wesley’s Conception and Use of Scripture, 46.
 See, Wesley, Sermons III, 556.
 Marquadt, John Wesley’s Social Ethics, 69.
 John Wesley “Letter to Granville Sharpe: Oct 111787” in The Letters of John Wesley, AM (8 vols.; Edited by John Telford. London: The Epworth Press, 1931), 8:17.
 Roy Hattersley, The Life of John Wesley: A Brand from the Burning ( London: Doubleday, 2002), 390.
 Hattersley, The Life of John Wesley, 390.
 Hattersley, The Life of John Wesley, 390-391.
 John Wesley, The Journal of the Reverend John Wesley A.M. (Vol 1 of The Journal of the Reverend John Wesley A.M; London: Wesleyan Conference Office, 1872), 40.
 Wesley, Journal Volume 1, 40.
 Hattersley, The Life of John Wesley, 112-113,
 Pollock, Wesley The Preacher, 240.
 John Wesley, Explanatory Notes on the Old Testament Volume 1, 272.
 Pollock, Wesley The Preacher, 258.
 Wesley, Journal Volume 1, 40.
 Wesley, Thoughts Upon the Slave Trade, ( IV.9), 41.
 Wesley, Thoughts upon the Slave Trade, (V. 7) 52.
 Thomas Clarkson, An Essay on the Slavery and Commerce of the Human Species, Particularly the African: 89.Cited 4th June 2008. Online: http://www.gutenberg.org/files/10611/10611-h/10611-h.htm.
 William Wilberforce, A letter on the abolition of the slave trade addressed to the freeholders and other inhabitants of Yorkshire (London: Cadel and Davis, 1807), 320.
 Colin Williams, John Wesley’s Theology Today (London: The Epworth Press, 1960), 33.
 See Jones, John’s Wesley’s Conception and Use of Scripture, 95.
 This definition appears in his sermon, “The Case for Reason Impartially Considered.” John Wesley, Sermons II 34-70 (vol. 2 of The Works of John Wesley; Edited by Albert C. Outler. Nashville: Abingdon Press, 1985), 590.
 Wesley, Sermons II 34-70, 592.
 Wilberforce, A Letter on Abolition of the Slave Trade, 320.
 Jones comments that changes in society “meant that the authority of the Bible was questioned as never before, and that even those who accepted its authority viewed it in a manner different from earlier periods. Hans Frei, in his Eclipse of Biblical Narrative, argues that this transition is best characterized as the loss of the narrative sense of Scripture. This new way of looking at the world no longer used the lenses of Scripture to see, but viewed Scripture itself as one more object to be investigated. The automatic certainty and authority of the sacred writings was no longer assumed, but had to be demonstrated in new ways.” Jones, John’s Wesley’s Conception and Use of Scripture, 27.
 Wesley is commenting here on Romans 1:19. John Wesley, Explanatory Notes upon the New Testament, (Repr. London: Epworth Press, 1976), 520.
 We will develop this in the next section.
 Wesley, Thoughts Upon Slavery, (IV.3), 31.
 Wesley, Thoughts Upon Slavery, (IV.3), 32.
 Wesley, Thoughts Upon Slavery, (IV.3), 33.
 Wesley, Thoughts Upon Slavery, (IV.4), 33.
 Judge Blackstone, cited in Wesley, Thoughts Upon Slavery, (IV.3), 1-32.
 Wesley, Thoughts Upon Slavery, (IV.3), 33.
 Wesley, Thoughts Upon Slavery, (IV.4), 33-34.
 (italics mine) Wesley, Thoughts Upon Slavery, (IV.1), 29.